The open time of emulsion paint is the time interval during which freshly applied paint can be blended with subsequently applied paint without the appearance of lack of uniformity. Under one approach, open time can be extended by adding volatile organic compounds (VOC) such as glycols into the emulsion paint formulation. However, environmental regulations limit the level of VOCs in paint compositions.
Currently, in many low VOC aqueous paints, open time becomes unacceptably short. Open time problems include, but are not limited to, skinning of left-open paints, not being able to cut back or blend in during brushing and rolling, and non-uniformity of sprayed surfaces. These problems are further exacerbated under fast dry conditions such as low humidity and high temperature.
Some attempts to improve open time involve modifying the aqueous paint composition during the manufacturing process. For example, U.S. Pat. No. 5,270,380 discloses a method for forming an aqueous coating by combining a latex polymer and a modifying compound having complementary reactable groups. U.S. Pat. No. 7,071,261 relates to aqueous paint compositions comprising a dispersion of polymeric nanoparticles that include amine functionality and at least one multi-ethylenically-unsaturated monomer. U.S. Pat. No. 7,569,636 discloses an aqueous coating composition comprising, among other things, a crosslinkable oligomer that provides improved open time and a dispersed polymer (e.g., in the form of a polymer latex) that reduces time to tack free dryness of the composition. U.S. Pat. No. 6,040,368 discloses an aqueous coating composition comprising an emulsion polymer that includes a copolymerized ethylenically unsaturated monomer such as acetoacetoxyethyl methacrylate (AAEM) to improve open time. U.S. Pat. No. 6,610,776 discloses aqueous emulsion paints, where the film forming emulsion latex polymer is copolymerized with a polyethylene glycol or polypropylene glycol to improve open time. US 2007/0249780 concerns a stabilizer composition comprising an uncrosslinked AB type polymer, where the A component can be polyphenoxy glycidyl ether, methylphenyl glycidyl ether, ethylphenyl glycidyl ether and the B component can be polyactalpolyether, acrylate, acrylamide and polyethylene oxide.
Some other attempts to improve open time use polyurethane. U.S. Pat. No. 6,303,189 discloses the addition of an aqueous polyurethane dispersion (PUD) to an aqueous coating composition having at least one film forming latex polymer, which is substantially un-crosslinked. US 2006/0148980 concerns polyurethane and polyurethane/acrylic hybrid dispersions formed from functional polyurethane and vinyl monomers including crosslinking agents to enhance the film formation and fast hardness development of the polyurethane.
Other attempts are directed at paint additives. US 2009/0227705 to Bochnick et al. discloses a latex open time extender wherein the acrylic or vinyl latex particles are polymerized with crosslinkable monomers. The latex particles are less than about 150 nm in size. US 2012/0165428 to Tilara discloses an open time extender comprising a neutralized water-soluble polymer having a hydrophilic, hydrophobic and crosslinkable monomers with a solid content less than about 20 wt. %.
Another method of improving open time involves the use of commercial paint extenders, which a consumer can add to a pre-manufactured aqueous latex paint. One latex-based paint extender on the market is Floetrol®, which is commercially available from the Flood Company of Hudson, Ohio. However, when Floetrol® is added to paints, the aqueous paints still tend to form skins, which are indicative of poor open time. Floetrol® also negatively affects water sensitivity and paint flow leveling. Furthermore, Floetrol® also does not provide compatibility with many commercial low-VOC latex paints since it can cause quick syneresis and separation. Floetrol® also reduces the gloss of higher sheen paints, such as semigloss and high gloss paints. Other commercially available open time additives include WonderWet™ IV and Optifilm™ OT1200. The commercially available open time additives may also negatively affect properties of paint films, such as scrubability and water sensitivity.
Thus, there remains a need for a paint open time extender that in addition to extending open time maintains/improves properties of paint films.